1. Field of the Invention
The present invention relates to a Voice over Internet Protocol (VoIP). More particularly, the present invention relates to an apparatus and a method for supporting Network Address Translation (NAT) traversal in a VoIP system.
2. Description of the Related Art
As Internet environments develop and various VoIP services are extended, the VoIP market is markedly expanding. Accordingly, the development of related technology and various research projects are in progress. In addition, as the VoIP market expands, a VoIP phone (also called an Internet phone or an IP phone) is being widely distributed.
Since the number of IP addresses available at the Internet is limited, a plurality of users share one IP address. For example, an Internet router generally used in a household allows a plurality of hosts to use the Internet by executing an NAT function of assigning private IP addresses to a plurality of hosts (e.g., a computer, a notebook, etc.) located at a lower end (Local Area Network (LAN) interface), and mapping the assigned IP addresses to a single public IP address given by a service provider to a user.
When an Internet phone is installed and used in various network environments, more particularly, in an NAT environment, an NAT traversal for an Internet phone is an essential factor because NAT has limitations. The NAT traversal allows communication with a terminal located in an NAT environment using a public IP address given in an Internet environment. The NAT traversal provides an NAT traversal solution for a VoIP signal and a media in a VoIP environment. The conventional method approaches the solution through system establishment on a network and providing a function to a VoIP phone. Representative examples include Simple Traversal of User Datagram Protocol (UDP) through NAT (STUN), Session Border Controller (SBC), etc.
The STUN is a protocol that can detect a type of NAT such as Symmetric NAT, Cone NAT, etc., and port mapping information. A client inside a private network requests connection from an STUN server before starting a session, and is assigned an IP address and a port number to be used by the client, and then uses the IP address and the port number during a session and media traffic transmission. However, STUN does not operate in Symmetric NAT, and an address obtained through the STUN is not useful for all peers and may not operate depending on a network state. That is, the STUN is a technique for allowing an end-terminal to search for existence and a type of NAT, and is a protocol formed based on a client-server model.
The SBC for providing an Internet multimedia service in a packet network is a network system for managing and processing a signal or a media message. In addition, the SBC is primarily used in a large-scale network environment for providing a VoIP service between service providers.
However, in the case where the STUN is applied to the VoIP service environment, there is a limitation that STUN client engines should be installed in all Internet phones and cooperate with an STUN server.
The SBC is a large-capacity system and is designed to provide cooperation between network providers in a VoIP service environment. Accordingly, it is limited in its application to small and medium-sized sites, especially regarding its costs. In addition, when a problem is generated from the SBC, since the problem may have an influence on all calls, it is difficult to guarantee stability of a VoIP service. Since both VoIP Private Branch eXchange (PBX) and SBC should be extended with respect to extension of a VoIP signal, there is a limitation of having dependency in supporting a protocol of SBC. That is, the SBC is a technique widely used between network providers or for a large-capacity site, and so is not suitable for an environment that uses a small and medium-sized VoIP PBX.
As described above, the conventional NAT traversal techniques have difficulties of having to add an Internet phone function and which increases the price of equipment in a network environment.
Therefore, an embedded Media Proxy Solution (eMPS) for providing an NAT traversal with respect to a media stream in a small and medium-sized VoIP PBX system is required.